AN ALLEGED YEAST POLYPHOSPHATE KINASE IS ACTUALLY DIADENOSINE-5',5'''-P-1,P-4-TETRAPHOSPHATE ALPHA,BETA-PHOSPHORYLASE

Polyphosphates are a major constituent of the yeast Saccharomyces cerevisiae. A purification of the enzyme polyphosphate kinase (E.C. 2.7.4.1) from this organism has been reported (Felter, S., and Stahl, A. J. C. (1973) Biochimie (Paris) 55, 245-251). The assay for activity used in this purification was the production of P-32-labeled nucleotide, presumed to be ATP, in the presence of [P-32]polyphosphate and ADP. We have found that this assay does not reflect the activity of a polyphosphate kinase but rather the combination of an exopolyphosphatase, releasing free [P-32]phosphate from the added [P-32]polyphosphate, and the ADP-[P-32]phosphate exchange activity of the enzyme diadenosine 5',5'''-P-1,P-4-tetraphosphate alpha,beta-phosphorylase (Ap(4)A phosphorylase). We also present direct evidence for the formation of an enzyme-AMP intermediate in the action of Ap(4)A phosphorylase.